Unless otherwise indicated herein, the approaches described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.
Human or animal skin is hygroscopic and permeable, such that water passes from inside a body through skin to the surrounding atmosphere via diffusion and evaporation or skin can absorb moisture from the surrounding atmosphere. The hygroscopic property of skin determines the health and cosmetic problems of the skin because the capability of skin for retaining moisture can be deteriorated when it is damaged through exposure to skin cosmetic products and exposure to ultraviolet radiation from the sun. Accordingly, it is important to precisely measure skin moisture content or hydration level to determine the overall health of skin or moisture content in skin so that one can assess possible cosmetic options and skin care options to maintain or improve the health of the skin. Also, the hydration measurement will be desirable for all cosmetic applications including formulation, support of efficacy claim and efficacy testing of skin care products.
Skin moisture measuring devices have been developed to detect the hydration level in skin, and have employed various techniques. One example method measures capacitance of a dielectric medium. This method measures the change in dielectric constant due to skin surface hydration changing the capacitance of a precision capacitor. The capacitance measurement can be conducted in a short period of time and may not be influenced by substances in the skin (for example, salts or residues of topical applied products). However, such measurement is conducted by using electrodes or probes attached to skin, which may impose stress on the skin. Further, although this method provides decent precision of moisture measurement, it is costly and may not be implemented in a portable size for individual users.